/*
 * jQuery appear plugin
 *
 * Copyright (c) 2012 Andrey Sidorov
 * licensed under MIT license.
 *
 * https://github.com/morr/jquery.appear/
 *
 * Version: 0.3.3
 */
(function($) {
    var selectors = [];
  
    var check_binded = false;
    var check_lock = false;
    var defaults = {
      interval: 250,
      force_process: false
    }
    var $window = $(window);
  
    var $prior_appeared;
  
    function process() {
      check_lock = false;
      for (var index = 0; index < selectors.length; index++) {
        var $appeared = $(selectors[index]).filter(function() {
          return $(this).is(':appeared');
        });
  
        $appeared.trigger('appear', [$appeared]);
  
        if ($prior_appeared) {
          var $disappeared = $prior_appeared.not($appeared);
          $disappeared.trigger('disappear', [$disappeared]);
        }
        $prior_appeared = $appeared;
      }
    }
  
    // "appeared" custom filter
    $.expr[':']['appeared'] = function(element) {
      var $element = $(element);
      if (!$element.is(':visible')) {
        return false;
      }
  
      var window_left = $window.scrollLeft();
      var window_top = $window.scrollTop();
      var offset = $element.offset();
      var left = offset.left;
      var top = offset.top;
  
      if (top + $element.height() >= window_top &&
          top - ($element.data('appear-top-offset') || 0) <= window_top + $window.height() &&
          left + $element.width() >= window_left &&
          left - ($element.data('appear-left-offset') || 0) <= window_left + $window.width()) {
        return true;
      } else {
        return false;
      }
    }
  
    $.fn.extend({
      // watching for element's appearance in browser viewport
      appear: function(options) {
        var opts = $.extend({}, defaults, options || {});
        var selector = this.selector || this;
        if (!check_binded) {
          var on_check = function() {
            if (check_lock) {
              return;
            }
            check_lock = true;
  
            setTimeout(process, opts.interval);
          };
  
          $(window).scroll(on_check).resize(on_check);
          check_binded = true;
        }
  
        if (opts.force_process) {
          setTimeout(process, opts.interval);
        }
        selectors.push(selector);
        return $(selector);
      }
    });
  
    $.extend({
      // force elements's appearance check
      force_appear: function() {
        if (check_binded) {
          process();
          return true;
        };
        return false;
      }
    });
  })(jQuery);